1. Field of the Invention
Embodiments in accordance with the present invention relate to methods and systems for a low-power, infrared-aided RTL System.
2. Description of Related Art
Real Time Location Systems (RTLS) have gained in popularity in the last few years. They found their way into many applications ranging from healthcare to schools, fleet location management and many other more specialized applications. RTLS offers enhanced resolution performance by use of secondary technologies such as infrared (IR), Ultrasound (US) and Low Frequency (LF). A spatial area within which secondary technologies is available may be referred to as a zone of influence. Secondary technologies add substantial burden on battery life of RTLS components.
Conventional RTL systems typically use radio frequency (RF) transmission to determine location. The RF-based methods may be augmented with infrared (IR) transmission as a localization method in order to improve accuracy to support room and sub-room level accuracies. An IR receiver typically is incorporated into a portable device (i.e., a tag) and IR transmitters are incorporated into base stations that are scattered in rooms and corridors within the enclosure. Typically, each the IR base stations transmits an identification (ID) to the portable devices, and the location of the portable devices is determined by their vicinity to a base station.
Embodiments in accordance with the present disclosure use virtual walls as described in U.S. Pat. No. 8,018,584 (“the '584 Patent”), which is hereby incorporated by reference in its entirety. The method of the '584 Patent emits IR toward one direction while noise is injected (i.e., transmitted) to another direction such that tags can receive only IR signals from the IR emitter pointed to their side of the virtual wall. This approach is very powerful but requires extra power for noise transmission
The basic advantages of synchronization of IR-based systems are described in U.S. Pat. No. 8,139,945 (“the '945 Patent”) and U.S. Pat. No. 8,604,909 (“the '909 Patent”), which are hereby incorporated by reference in their entirety. Timing synchronization information is transmitted using a plurality of stationary IR base stations and a plurality of portable devices (e.g., portable tags). Each IR base station is configured to receive the timing synchronization information and to transmit a corresponding IR location code in a time period, based on the received timing synchronization information. Improved synchronization allows a tag to activate certain circuitry only when it may be needed. In the '945 Patent, in order to synchronize the end devices (i.e., tags and exciters), a return link is used back from the system (e.g., an AP) to the end devices. The conventional CCX protocol is incapable of supporting the return link because the CCX protocol is one-directional.
In the '945 Patent, each portable device is configured: 1) to receive the timing synchronization information; 2) to detect the IR location codes from the IR base stations; and 3) to transmit an output signal including a portable device ID representative of the portable device and the detected IR location code. Each portable device is synchronized to detect the IR location code in the time period based on the received timing synchronization information. The '945 Patent enables coexistence of multiple IR transmitters at the same physical space, the construction of virtual walls, as well as facilitating high tag update rate with extremely low power consumption for portable tags.
If a tag is within IR communication range of more than one IR base station, it is preferable to communicate with the closest IR base station and/or the IR base station providing the strongest received signal to the tag, and at a low cost. However, known low-cost IR receivers do not provide a direct output of received IR signal strength. Therefore, a need exists to provide low-cost calculation of received IR signal strength.